Ferroelectric memory having a refresh control circuit capable of recovering residual polarization of unselected memory cells

Abstract

A memory wherein any “disturb effect” can be suppressed in which data in unselected memory cells are lost. This memory has a memory cell array ( 1 ) including bit lines, word lines, which are disposed to intersect the bit lines, and memory cells ( 12 ) each connected between bit and word lines. In this memory, an access operation, which includes at least one of read, rewrite and write operations, is made to a selected memory cell ( 12 ). During this access operation, it is performed to apply to the memory cell ( 12 ) a first voltage pulse, which provides an electrical field in a first direction so as to invert a stored data, and a second voltage pulse, which provides as electrical field in the opposite direction to the first one so as not to invert the stored data. In addition, a recovery operation for recovering a residual polarization amount is made to the memory cell ( 12 ).

1. A memory, comprising:
 a memory cell array including a bit line, a word line arranged to intersect with the bit line, and a first memory cell connected between the bit line and the word line; and 
 a refresh control circuit; 
 wherein the refresh control circuit is configured to apply, to the first memory cell through an access operation, a first voltage pulse that provides an electrical field in a first direction to invert stored data and a second voltage pulse that provides an electrical field in a second direction, opposite to the first direction, to not invert stored data; 
 wherein the access operation includes at least one of a read operation, a rewrite operation, or a write operation to be performed on a selected memory cell; and 
 wherein the refresh control circuit is further configured to perform a recovery operation on the first memory cell to recover a quantity of residual polarization. 
 
     
     
       2. The memory of  claim 1 , wherein the refresh control circuit is further configured to perform the recovery operation to maintain a quantity of residual polarization in an arbitrary memory cell of the memory cell array. 
     
     
       3. The memory of  claim 2 , wherein the refresh control circuit is further configured to perform the recovery operation after deterioration of the quantity of residual polarization in the arbitrary memory cell exceeds a prescribed quantity. 
     
     
       4. The memory of  claim 1 , wherein:
 the first memory cell comprises an unselected memory cell; and 
 the refresh control circuit is further configured to perform the recovery operation by varying a technique used to apply the first voltage pulse and the second voltage pulse to the first memory cell based on whether data read by the read operation is first data or second data. 
 
     
     
       5. The memory of  claim 4 , wherein the refresh control circuit is further configured to perform the recovery operation by applying the first voltage pulse and the second voltage pulse to the first memory cell at same respective frequencies as frequencies of the read and rewrite operations performed on the selected memory cell. 
     
     
       6. The memory of  claim 1 , wherein the refresh control circuit is further configured to perform the recovery operation one by one on all memory cells linked to a word line of the selected memory cell. 
     
     
       7. The memory of  claim 1 , wherein the refresh control circuit is further configured to collectively perform the recovery operation on all memory cells linked to a word line of the selected memory cell. 
     
     
       8. The memory of  claim 1 , wherein the refresh control circuit comprises a recovery operation control circuit configured to start the recovery operation on the first memory cell if deterioration of the quantity of residual polarization in the first memory cell exceeds a prescribed quantity. 
     
     
       9. The memory of  claim 8 , further comprising:
 a dummy cell, wherein the refresh control circuit is further configured to apply to the dummy cell a third voltage pulse providing an electrical field in the first direction and having a voltage substantially identical to the first voltage pulse and a fourth voltage pulse providing an electrical field in the second direction and having a voltage substantially identical to the second voltage pulse, and wherein the refresh control circuit is further configured to apply the third voltage pulse and the fourth voltage pulse in correspondence with the application of the first voltage pulse and the second voltage pulse to the first memory cell; 
 wherein the recovery operation control circuit is configured to start the recovery operation on the first memory cell if deterioration of a quantity of residual polarization in the dummy cell exceeds a prescribed quantity. 
 
     
     
       10. The memory of  claim 1 , wherein:
 the first memory cell comprises a ferroelectric capacitor; 
 the memory is configured to apply a high-voltage voltage pulse having a prescribed pulse width to the selected memory cell while applying a low-voltage voltage pulse having the prescribed pulse width to the first memory cell at least either in the access operation or in the recovery operation; and 
 the memory is further configured to set the prescribed pulse width to a pulse width causing polarization inversion if the memory applies the high-voltage voltage pulse to the ferroelectric capacitor, while substantially causing no polarization inversion if the memory applies the low-voltage voltage pulse to the ferroelectric capacitor.